Apparatuses and methods for duty cycle adjustments

ABSTRACT

Apparatuses and methods have been disclosed. One such apparatus includes a plurality of gates coupled together in series. A first pull-down circuit can be coupled to a node between two adjacent gates of the plurality of gates and controlled responsive to a first control signal. A second pull-down circuit can be coupled to an output of one of the gates and controlled responsive to a second control signal. A duty cycle of a signal provided by the plurality of gates can be increased responsive to the first control signal and can be decreased responsive to the second control signal. The plurality of gates and the first and second pull-down circuits can make up a duty cycle adjuster circuit that can adjust the duty cycle of the signal by adjusting only a single type of edges of the signal.

BACKGROUND

Apparatuses such as electronic devices can have a clock circuit that cangenerate a clock signal to synchronize at least certain circuits withinthe electronic device. Certain electronic devices (e.g., memory devices)that employ these clock circuits can be manufactured to meet certaintiming standards. Thus, a memory device that includes a clock circuitcan generate a clock signal to meet a particular timing standard inorder to be compatible with other electronic devices that interact withthe memory device.

A signal might be generated with relatively small timing inaccuraciesand/or a clock path of a circuit can introduce timing inaccuracies intothe signal. These timing inaccuracies can be corrected by a duty cycleadjuster circuit (e.g., a duty cycle correction circuit) that can adjustthe duty cycle of a clock signal. However, a problem with conventionalduty cycle adjuster circuits is that they adjust falling edges of theclock signal to increase duty cycle, but then have to adjust risingedges of the clock signal to decrease the duty cycle. Also, when therising edges of the clock signal are adjusted, it can impact timing andjitter performance by introducing accuracy mismatches and increasingpower and lock time budgets.

FIGS. 1A and 1B illustrate typical prior art duty cycle adjustercircuits. FIG. 1A shows a schematic diagram of a circuit that canincrease the duty cycle of a clock signal as shown by adjusting (e.g.,skewing) the falling edges of the clock signal. A low signal on a firstinverter 101 is inverted to a high signal that is inverted back to a lowsignal at the output of the circuit by a second inverter 102. However,the CLK OUT low signal is delayed by the gate delays resulting from thetwo inverters 101, 102. Thus, the resulting high signal at the node 110between the inverters 101, 102 during that delay can enable then-channel metal-oxide semiconductor (NMOS) transistors 103, 104 whentheir control gates are properly biased. A control signal on the firsttransistor 103 can then enable that transistor 103 and the resultingdelayed high signal from the CLK OUT can enable the second transistor104 such that the node between the two inverters is pulled down. Thisresulting low signal is inverted to a high signal at CLK OUT, thusadjusting the falling edges of the output clock CLK OUT.

FIG. 1B shows a circuit that can decrease the duty cycle of a clocksignal as shown by adjusting the rising edges of the clock signal. Thefirst two inverters 121, 122 provide (e.g., produce, generate, output,etc.) a substantially similar signal at the middle node 127 as the inputclock CLK IN except delayed by two gate delays from the inverters 121,122. A third inverter 123 provides an inverted clock signal that isdelayed by yet another gate delay caused by the third inverter 123.These delays provide a high signal at the middle node 127 atsubstantially the same time that the control gates of NMOS transistors125, 126 are biased with enable voltages from a control signal and thedelayed signal from the third inverter 123. When these transistors 125,126 turn on, they pull down the middle node 127 when normally that nodewould be going high, thus adjusting the rising edges of the output clockCLK OUT. However, such an adjustment of the duty cycle using the risingedges can introduce timing problems with certain standards and jitterperformance problems.

There are general needs to adjust a signal duty cycle to deal withtiming and jitter performance problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate schematic diagrams of typical prior art dutycycle correction circuits.

FIG. 2 illustrates a schematic diagram of an embodiment of a duty cycleadjuster circuit.

FIG. 3 illustrates an embodiment of a timing diagram for a duty cycleincrease operation in accordance with the embodiment of FIG. 2.

FIG. 4 illustrates an embodiment of a timing diagram for a duty cycledecrease operation in accordance with the embodiment of FIG. 2.

FIG. 5 illustrates a schematic diagram of another embodiment of a dutycycle adjuster circuit.

FIG. 6 illustrates an embodiment of a timing diagram for a duty cycledecrease operation in accordance with the embodiment of FIG. 5.

FIG. 7 illustrates an embodiment of a timing diagram for a duty cycleincrease operation in accordance with the embodiment of FIG. 5.

FIG. 8 illustrates another embodiment in accordance with the embodimentsof FIGS. 2 and 4.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof and in which is shown, byway of illustration, specific embodiments. In the drawings, likenumerals describe substantially similar components throughout theseveral views. Other embodiments may be utilized and structural,logical, and electrical changes may be made without departing from thescope of the present disclosure.

The following embodiments include duty cycle adjuster circuits that canadjust the duty cycle of an output signal by adjusting only a singletype of edges (e.g., just the falling edges or just the rising edges) ofthe output signal. For example, whether the duty cycle is to beincreased or decreased, only a single type of edges (e.g., either thefalling edges or the rising edges, but not both) of the signal isadjusted or vice versa.

FIG. 2 illustrates a schematic diagram of an embodiment of a duty cycleadjuster circuit. This circuit includes a plurality of series coupledgates 201-204 (e.g., inverters). At an INF node, a first pair oftransistors 200 (e.g., NMOS) are coupled together in series between theINF node and a reference voltage node (e.g., circuit ground). Thecollector of a first transistor 205 of the first pair of transistors 200is coupled to the INF node, the collector of a second transistor 206 iscoupled to the drain of the first transistor 205, and the drain of thesecond transistor 206 is coupled to the reference voltage node. Inanother embodiment, the first transistor 205 and the second transistor206 can swap locations.

At the output CLK OUT, a second pair of transistors 220 (e.g., NMOS) arecoupled together in series between the CLK OUT output and the referencevoltage node. The collector of a first transistor 207 of the second pairof transistors 220 is coupled to the CLK OUT output, the collector of asecond transistor 208 is coupled to the drain of the first transistor207, and the drain of the second transistor 208 is coupled to thereference voltage node. The first and second pairs of transistors 200,220 can act as pull-down circuits.

The circuit can receive an input signal CLK IN, provide an output signalCLK OUT, and be responsive to a bias increase control signal BIASINC anda bias decrease control signal BIASDEC. The BIASINC signal is coupled toa control gate of and enables/disables the first transistor 205 of thefirst pair of transistors 200. The BIASDEC signal is coupled to acontrol gate of and enables/disables the first transistor 207 of thesecond pair of transistors 220.

The BIASINC and BIASDEC control signals are shown in the embodiments ofFIGS. 2 and 5 as being analog voltage signals coupled to the controlgates of their respective transistors. However, another embodiment canincorporate digital, multiple bit bias increase and decrease controlsignals as shown in FIG. 8 and described subsequently.

In the embodiment of FIG. 2, the BIASINC and BIASDEC signals are bothactive high. A high signal level can be any voltage that is at least atthe threshold voltage of the respective transistor in order to enablethe transistor such that it conducts. A low signal level can be anyvoltage that is less than the threshold voltage of the respectivetransistors such that the transistor is disabled and does not conduct.Thus, when it is desired to increase the duty cycle of the outputsignal, the BIASINC signal can be increased to a high level while theBIASDEC signal is at a low level. When it is desired to decrease theduty cycle, the BIASINC signal can be at a low level while the BIASDECsignal can be increased to a high level. Other embodiments can use bothactive low BIASINC and BIASDEC signals or a combination of active highand active low signals.

The control gate of the second transistor 206 of the first pair oftransistors 200 is coupled to a CNTL node between two of the inverters202, 203. The control gate of the second transistor 208 of the secondpair of transistors 220 is coupled to the INF node.

FIG. 3 illustrates an embodiment of a timing diagram for a duty cycleincrease operation of the circuit of FIG. 2. The timing diagram showsonly a single pulse for purposes of clarity. However, one skilled in theart would realize that the circuit of FIG. 2 would work the same with asignal comprising a plurality of pulses.

Referring to both FIG. 2 and FIG. 3, the CLK IN pulse is shown goingfrom a low level to a high level into the first gate 201. The output ofthe first gate 201 is the INF node that is shown going to a low level.The low-going INF signal is delayed from the CLK IN signal by one gatedelay.

The INF signal is input to the second gate 202 that can then invert itand generate the CNTL signal at the CNTL node. This signal is delayedfrom the CLK IN signal by two gate delays and is used to control thesecond transistor 206. When the CNTL signal reaches a threshold voltagefor the second transistor 206, the second transistor 206 can turn on andconduct when both the first transistor 205 is turned on and when the INFsignal reaches a collector voltage high enough above the reference.Thus, when the BIASINC signal is high, the INF signal is high, and theCNTL signal is high, the INF node can be pulled down. FIG. 3 shows thetime 301 on the CNTL signal where, due to the gate delays, the CNTLsignal and the INF signal would be high substantially simultaneously.The time 300 where the INF signal is pulled low is shown matching upwith the time 301 of the CNTL signal.

The delay of the rising edge of the INF signal going high at area 300can cause the CLK OUT signal to be delayed as well. This has the effectof moving the falling edge of CLK OUT by a particular time representedby ΔT′. The delay of the rising edge of the INF signal can be controlledby the BIASINC signal.

As shown in FIG. 2, ΔT′ can be determined by the quantity of gates(e.g., gate delay) between the INF node and the output of the circuit.Thus, in order to change the amount ΔT′ by which the CLK OUT signal canbe adjusted, the quantity of gates between the INF node and the outputof the circuit can be changed. Increasing the quantity of gates canincrease ΔT′ and decreasing the quantity of gates can decrease ΔT′.

During the duty cycle increase operation, the second pair of transistors220 are turned off since BIASDEC is at a low level. Thus, this circuit220 has no affect on the CLK OUT signal at this time.

The above described embodiment assumes a digital implementation of theembodiment of FIG. 2. In other words, when the BIASINC signal is alogical high state (e.g., at threshold voltage of transistor 205), thetransistor 205 is turned on. However, FIG. 2 can also operate in ananalog implementation. In such an embodiment, the voltage level of theBIASINC signal above the threshold voltage of transistor 205 candetermine the amount of adjustment of the duty cycle. Thus, increasingthe voltage level of the BIASINC signal will increase ΔT′. For example,if the threshold level of transistor 205 is 0.5V, any voltage level forBIASINC that is above 0.5V will increase ΔT′.

Additionally, the strength of the pull down of the first pair oftransistors 200 can affect the duty cycle change. The inverter 201includes an internal pull up resistor (not shown). The ratio of the pulldown, effected by the first pair of transistors 200, to the pull up ofthe internal pull up resistor of inverter 201 can adjust the duty cycle.For example, increasing the BIASINC voltage level can increase the pulldown strength and, thus, increase ΔT′.

FIG. 4 illustrates a timing diagram of an embodiment of a duty cycledecrease operation of the circuit of FIG. 2. The timing diagram showsonly a single pulse for purposes of clarity. However, one skilled in theart would realize that the circuit of FIG. 2 would work the same with asignal comprising a plurality of pulses.

Referring to both FIG. 2 and FIG. 4, the CLK IN pulse is shown goingfrom a low level to a high level into the first gate 201. The output ofthe first gate 201 is the INF node that is shown going to a low level.The low-going INF signal is delayed from the CLK IN signal by one gatedelay. ΔT is the maximum duty cycle increase amount. The duty cycleincrease is controlled by the strength ratio of pull down 220

The INF signal is input to the second gate 202 that can then invert itand generate the CNTL signal at the CNTL node. The INF signal can alsobe used to control the second transistor 208 of the second pair oftransistors 220. When the INF signal reaches a threshold voltage for thesecond transistor 208, the second transistor 208 can turn on and conductwhen both the first transistor 207 of the pair of transistors 220 isturned on and when the CLK OUT signal reaches a collector voltage highenough above the reference. Thus, when the BIASDEC signal is high, theINF signal is high, and the CLK OUT signal is high, the CLK OUT outputnode can be pulled down by the second pair of transistors 220 at a timeΔT prior to when the CLK OUT signal would normally go low. FIG. 4 showsthe point 401 on the CLK OUT signal where, due to the gate delays, theCLK OUT signal and the INF signal would be high substantiallysimultaneously.

As in the duty cycle increase embodiment above, the time period ΔT′ thatthe duty cycle can be decreased can be determined by the quantity ofgates (e.g., gate delay) between the INF node and the output of thecircuit. Thus, in order to change the amount ΔT′ by which the CLK OUTsignal can be adjusted, the quantity of gates between the INF node andthe output of the circuit can be changed. Increasing the quantity ofgates can increase ΔT′ and decreasing the quantity of gates can decreaseΔT′.

During the duty cycle decrease operation, the first pair of transistors200 are turned off since BIASINC is at a low level. Thus, this circuit200 has no affect on the CLK OUT signal at this time.

The above described embodiment in FIG. 4 assumes a digitalimplementation of the embodiment of FIG. 2. In other words, when theBIASDEC signal is a logical high state (e.g., at threshold voltage oftransistor 207), the transistor 207 is turned on. However, FIG. 2 canalso operate in an analog implementation. In such an embodiment, thevoltage level of the BIASDEC signal above the threshold voltage oftransistor 207 can determine the amount of adjustment of the duty cycle.Thus, increasing the voltage level of the BIASDEC signal will decreaseΔT′. For example, if the threshold level of transistor 207 is 0.5V, anyvoltage level for BIASDEC that is above 0.5V will decrease ΔT′.

Additionally, the strength of the pull down of the second pair oftransistors 220 can affect the duty cycle change. The inverter 204includes an internal pull up resistor (not shown). The ratio of the pulldown, effected by the second pair of transistors 220, to the pull up ofthe internal pull up resistor of inverter 204 can adjust the duty cycle.For example, increasing the BIASDEC voltage level can increase the pulldown strength and, thus, decrease ΔT′.

FIG. 5 illustrates another embodiment of a duty cycle adjuster circuit.This embodiment enables a range of time for the duty cycle adjustment.This range can be illustrated in FIG. 5 as a time period between ΔT₁ andΔT₂. The ΔT₁ and ΔT₂ times can be the same or different. As seen in thecircuit of FIG. 5, ΔT₁ can be adjusted by the quantity of gates (e.g.,gate delay) between the input node CLK IN and a CF node. Similarly, ΔT₂can be adjusted by the quantity of gates between the output node CLK OUTand an INF node. ΔT₁+ΔT₂ indicates a maximum range of duty cycle changeamount.

The circuit of FIG. 5 comprises a plurality of gates 501-504 (e.g.,inverters) coupled in series. At an INF node, a first pair oftransistors 500 (e.g., NMOS) are coupled together in series between theINF node and a reference voltage node (e.g., circuit ground). Thecollector of a first transistor 510 of the first pair of transistors 500is coupled to the INF node, the collector of a second transistor 511 iscoupled to the drain of the first transistor 510, and the drain of thesecond transistor 511 is coupled to the reference voltage.

At the output CLK OUT, a second pair of transistors 520 (e.g., NMOS) arecoupled together in series between the CLK OUT output and the referencevoltage node. The collector of a first transistor 512 of the second pairof transistors 520 is coupled to the CLK OUT output, the collector of asecond transistor 513 is coupled to the drain of the first transistor512, and the drain of the second transistor 513 is coupled to thereference voltage node.

At a CF node, a third pair of transistors 530 (e.g., PMOS) are coupledbetween the CF node and a voltage source node (e.g., supply voltagenode). The collector of a first transistor 514 of the third pair oftransistors 530 is coupled to the voltage source node, the collector ofa second transistor 515 is coupled to the drain of the first transistor514, and the drain of the second transistor 515 is coupled to the CFnode. The first and second pairs of transistors 500, 520 can act aspull-down circuits while the third pair of transistors 530 can act as apull-up circuit.

The circuit can receive an input signal CLK IN, provide an output signalCLK OUT, and be responsive to a bias increase control signal BIASINC,and a bias decrease control signal BIASDEC. The BIASINC signal iscoupled to a control gate of and enables/disables the first transistor510 of the first pair of transistors 500 and the first transistor of thethird pair of transistors 530. The BIASDEC signal is coupled to acontrol gate of and enables/disables the first transistor 512 of thesecond pair of transistors 520.

In a digital implementation of the embodiment of FIG. 5, the BIASINC andBIASDEC signals are both active high. A high signal level can be anyvoltage that is at least at the threshold voltage of the respectivetransistor in order to enable the transistor such that it conducts. Alow signal level can be any voltage that is less than the thresholdvoltage of the respective transistors such that the transistor isdisabled and does not conduct. Thus, when it is desired to increase theduty cycle of the output signal, the BIASINC signal can be increased toa high level while the BIASDEC signal is at a low level. When it isdesired to decrease the duty cycle, the BIASINC signal can be at a lowlevel while the BIASDEC signal can be increased to a high level. Otherembodiments can use active low BIASINC and BIASDEC signals or acombination of active high and active low signals.

The control gate of the second transistor 511 of the first pair oftransistors 500 is coupled to a CNTL node between two of the gates 502,503. The control gate of the second transistor 513 of the second pair oftransistors 520 is coupled to the INF node. The control gate of thesecond transistor 514 of the third pair of transistors 530 is coupled tothe input CLK IN. Using the types of transistors illustrated in FIG. 5,each of the second transistors 511, 513 of the first and second pairs oftransistors 500, 520 can be enabled by a high signal while the secondtransistor 514 of the third pair of transistors 530 can be enabled by alow signal.

In an analog implementation of the embodiment of FIG. 5, the voltagelevel of the BIASINC signal above the threshold voltage of transistor510 can determine the amount of adjustment of the duty cycle. Thus,increasing the voltage level of the BIASINC signal will increase ΔT′.For example, if the threshold level of transistor 510 is 0.5V, anyvoltage level for BIASINC that is above 0.5V will increase ΔT′.

Additionally, the strength of the pull down of the first pair oftransistors 500 can affect the duty cycle change. The inverter 501includes an internal pull up resistor (not shown). The ratio of the pulldown, effected by the first pair of transistors 500, to the pull up ofthe internal pull up resistor can adjust the duty cycle. For example,increasing the BIASINC voltage level above the transistor 510 thresholdlevel can increase the pull down strength and, thus, increase ΔT′.

Similarly, in an analog implementation of the embodiment of FIG. 5, thevoltage level of the BIASDEC signal above the threshold voltage oftransistor 512 can determine the amount of adjustment of the duty cycle.Thus, increasing the voltage level of the BIASDEC signal will decreaseΔT′. For example, if the threshold level of transistor 512 is 0.5V, anyvoltage level for BIASINC that is above 0.5V will decrease ΔT′.

Additionally, the strength of the pull down of the second pair oftransistors 520 can affect the duty cycle change. The inverter 504includes an internal pull up resistor (not shown). The ratio of the pulldown, effected by the second pair of transistors 520, to the pull up ofthe internal pull up resistor can adjust the duty cycle. For example,increasing the BIASDEC voltage level above the transistor 512 thresholdlevel can increase the pull down strength and, thus, decrease ΔT′.

FIG. 6 illustrates an embodiment of a timing diagram for a duty cycleincrease operation of the circuit of FIG. 5. The timing diagram showsonly a single pulse for purposes of clarity. However, one skilled in theart would realize that the circuit of FIG. 5 would work the same with asignal comprising a plurality of pulses.

Referring to both FIG. 5 and FIG. 6, the CLK IN pulse is shown goingfrom a low level to a high level into the first gate 501. The output ofthe first gate 501 is the INF node that is shown going to a low level.The low-going INF signal is delayed from the CLK IN signal by one gatedelay.

The INF signal is input to the second gate 502 that can then invert itand generate the CNTL signal at the CNTL node. This signal is delayedfrom the CLK IN signal by two gate delays and is used to control thesecond transistor 511. When the CNTL signal reaches a threshold voltagefor that transistor 511, the transistor 511 can turn on and conduct whenboth the first transistor 510 is turned on and when the INF signalreaches a collector voltage high enough above the reference. Thus, whenthe BIASINC signal is high, the INF signal is high, and the CNTL signalis high, the INF node can be pulled down. FIG. 6 shows the time 601 onthe CNTL signal where, due to the gate delays, the CNTL signal and theINF signal would be high substantially simultaneously. The time 600where the INF signal is pulled low is shown matching up with the time601 of the CNTL signal.

The delay of the INF signal going high at point 600 can cause the CLKOUT signal to be delayed as well. This has the effect of moving thefalling edge of CLK OUT by a particular time represented by ΔT′.

During the duty cycle increase operation, the second pair of transistors520 and the third pair of transistors 530 are turned off since BIASDECis at a low level such that the first transistor 512 is turned off andBIASINC is at a high level such that the first transistor 515 is turnedoff (the PMOS transistor 515 is enabled with an active low signal).Thus, the second 520 and third pairs of transistors 520, 530 have noaffect on the CLK OUT signal during this operation.

FIG. 7 illustrates an embodiment of a timing diagram for a duty cycledecrease operation of the circuit of FIG. 5. The timing diagram showsonly a single pulse for purposes of clarity. However, one skilled in theart would realize that the circuit of FIG. 5 would work the same with asignal comprising a plurality of pulses.

Referring to both FIG. 5 and FIG. 7, the CLK IN pulse is shown goingfrom a low level to a high level into the first gate 501. The output ofthe first gate 501 is the INF node that is shown going to a low level.The low-going INF signal is delayed from the CLK IN signal by one gatedelay.

The INF signal is input to the second gate 502 that can then invert itand generate the CNTL signal at the CNTL node. The INF signal can alsobe used to control the second transistor 513 of the second pair oftransistors 520. When the INF signal reaches a threshold voltage forthat transistor 513, the transistor 513 can turn on and conduct whenboth the first transistor 512 of the pair of transistors 520 is turnedon and when the CLK OUT signal reaches a collector voltage high enoughabove the reference. This has the effect of pulling the output down at atime ΔT₂ from when it normally would go low. Additionally, since theBIASINC signal is low during this operation, the third pair transistors530 can conduct when both the CLK IN signal are low and the CF node goeslow. This has the effect of pulling the CF node high at a time ΔT₁ priorto when the CF node would normally go high. Thus, the duty cycle can beadjusted in the range approximately between ΔT₁ and ΔT₂. The range 700when these signals are true is indicated in FIG. 7.

In the embodiment of FIG. 5, since the quantity of gates that determineΔT₁ is equal to the quantity of gates that determine ΔT₂, ΔT₁=ΔT₂. Byincreasing the quantity of gates between the INF node and the output,ΔT₂ can be increased. By increasing the quantity of gates between theinput and the CF node, ΔT₁ can be increased. In order to keep propersignal level for each node when increasing and decreasing the quantityof gates, the INF node can be located after a first odd number of gates,the CNTL node can be located after first even number of gates, the CFnode can be located after a second odd number of gates, and the CLK OUToutput can be located after a second even number of gates where thesecond odd number of gates is greater than first odd number of gates andthe second even number of gates is greater than the first even number ofgates.

FIG. 8 illustrates an embodiment of any of the first or secondtransistor pairs 200, 202, 500, 502 of FIG. 2 or 5. As discussedpreviously, the circuits of those figures used an analog voltage signalto enable/disable the first transistors 205, 207, 510, 512 in the pairof transistors 200, 202, 500, 502. The embodiment of FIG. 8 can use amultiple bit, digital control signal to control the duty cycle adjustercircuits.

The embodiment of FIG. 8 comprises a plurality of transistors 800-803connected in parallel that together act as the first transistors of theabove circuits. The control gates of each transistor 800-803 can becoupled to a different enable signal. Thus, a four bit control wordcomprising BIAS₀, BIAS₁, BIAS₂, BIAS₃ can be used to control the circuit(assuming the second transistor 810 is enabled as described previously).The active state of each enable signal can be determined by the type oftransistor (e.g., NMOS, PMOS) used as each of the parallel coupledtransistors 800-803.

For example, a 1111 control word provided to the circuit illustrated inFIG. 8 would enable all of the transistors 800-803 if the transistorswere NMOS transistors that can be enabled with an active high signal. Ifthe second and fourth transistors 801, 803 were replaced with PMOStransistors, however, a 0000 control word would enable all of thetransistors 800-803.

In an analog implementation of the embodiment of FIG. 8, the voltagelevel of the BIAS₀-BIAS₃ signals above the threshold voltage of theirrespective transistors 800-803 can determine the amount of adjustment ofthe duty cycle. Thus, increasing the voltage level of the BIAS₀-BIAS₃signals will increase ΔT′. For example, if the threshold level oftransistor 800 is 0.5V, any voltage level for BIAS₀ that is above 0.5Vwill increase ΔT′.

Additionally, the strength of the pull down of any one of the pluralityof transistors 800-803 can affect the duty cycle change. The ratio ofthe pull down, effected by the plurality of transistors 800-803, to thepull up of an internal pull up resistor of any gate coupled to the INFnode can adjust the duty cycle. For example, increasing the BIAS₀voltage level above the transistor 800 threshold level can increase thepull down strength and, thus, increase ΔT′.

The above embodiments illustrate the transistors as being NMOStransistors. Other embodiments can use PMOS transistors.

Accordingly, the quantity and types of transistors shown in FIG. 8 arefor purposes of illustration only. The quantities and types oftransistors can determine the control word content and size.

As used herein, an apparatus may refer to, for example, circuitry, anintegrated circuit die, a memory device, a memory array, or a systemincluding such a circuit, die, device or array.

CONCLUSION

One or more embodiments of the duty cycle adjuster circuit can adjust asingle type of edges of a signal in order to both increase and decreasea duty cycle. This can result in better jitter performance and outputdata eye window in a system by eliminating a duty cycle variable on ajitter source due to a rising edge timing being adjusted. The presentembodiments can also provide energy efficiency advantages over the priorart by saving power on digital locked loop control logic by providing amore predictable locking time.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations willbe apparent to those of ordinary skill in the art. Accordingly, thisapplication is intended to cover any adaptations or variations.

1. An apparatus comprising: a plurality of logic gates coupled inseries; a first pull-down circuit coupled to a first node between twoadjacent logic gates of the plurality of logic gates and controlledresponsive to a first control signal; a pull-up circuit coupled to asecond node between two adjacent logic gates of the plurality of logicgates, wherein the first node is coupled to a logic gate output after afirst odd number of the logic gates and the second node is coupled to agate output after a second odd number of the logic gates where thesecond odd number is greater than the first odd number; and a secondpull-down circuit coupled to an output of one of the logic gates andcontrolled responsive to a second control signal, wherein a duty cycleof a signal provided by the plurality of logic gates is increasedresponsive to the first control signal and decreased responsive to thesecond control signal.
 2. The apparatus of claim 1 wherein the pluralityof logic gates comprises a plurality of inverter gates.
 3. The apparatusof claim 1 wherein each of the first and second pull-down circuitscomprise a plurality of transistors coupled in series.
 4. The apparatusof claim 3 wherein the node is a first node and the first pull-downcircuit comprises: a first transistor coupled between the first node anda second transistor, a control gate of the first transistor to receivethe first control signal; and the second transistor coupled between thefirst transistor and a reference voltage node, the second transistorhaving a control gate coupled to a second node between two adjacentgates of the plurality of gates.
 5. The apparatus of claim 3 wherein atime that the duty cycle of the signal is increased is determined by avoltage to be applied to a transistor of the first pull-down circuit. 6.The apparatus of claim 3 wherein the time that the duty cycle of thesignal is decreased is determined by a voltage to be applied to atransistor of the second pull-down circuit.
 7. The apparatus of claim 1wherein the node is a first node and the duty cycle of the signal isadjusted within a time range indicated by a time period between ΔT₁ andΔT₂, wherein ΔT₁ is determined by a gate delay between an input of theplurality of logic gates and a second node and ΔT₂ is determined by agate delay between the first node and the output of the one of the logicgates.
 8. (canceled)
 9. (canceled)
 10. The apparatus of claim 1 whereinthe first and second pull-down circuits each comprise first and secondtransistors coupled together in series and further comprising: a controlgate of the first transistor of the first pull-down circuit to receivethe first control signal; a control gate of the second transistor of thefirst pull-down circuit coupled to a third node located after an evennumber of the gates of the plurality of logic gates; a control gate ofthe first transistor of the second pull-down circuit to receive thesecond control signal; and a control gate of the second transistor ofthe second pull-down circuit coupled to the first node.
 11. Theapparatus of claim 10, wherein the pull-up circuit comprises first andsecond transistors coupled together in series and further comprising: acontrol gate of the first transistor of the pull-up circuit to receivethe first control signal; and a control gate of the second transistor ofthe pull-up circuit coupled to an input of the plurality of logic gates.12. The apparatus of claim 1 wherein each of the first and secondpull-down circuits comprises: a plurality of first transistors coupledtogether in parallel, a control gate of each of the plurality oftransistors coupled to a different enable signal of the respectivecontrol signal; and a second transistor coupled between the plurality offirst transistors and a reference node.
 13. The apparatus of claim 1,wherein the plurality of logic gates and the first and second pull-downcircuits comprise a duty cycle adjuster circuit that can adjust the dutycycle of the signal by adjusting only a single type of edges of thesignal.
 14. The apparatus of claim 1, wherein the plurality of logicgates and the first and second pull-down circuits comprise a duty cycleadjuster circuit that can increase the duty cycle of the signal byadjusting falling edges of the signal responsive to the first controlsignal.
 15. The apparatus of claim 14, wherein the duty cycle adjustercan also decrease the duty cycle of the signal by adjusting the fallingedges of the signal responsive to the second control signal. 16-20.(canceled)
 21. The apparatus of claim 12 wherein the plurality of firsttransistors coupled together in parallel comprise a plurality of controlgates coupled to a plurality of enable signals, each control gatecoupled to a different enable signal.
 22. The apparatus of claim 21wherein each of the first and second pull-down circuits is selectivelyenabled in response to a control word configured to act as the pluralityof enable signals.
 23. The apparatus of claim 22 wherein the duty cycleis determined in response to voltage levels of each of the plurality ofenable signals.
 24. The apparatus of claim 23 wherein the duty cycle isadjusted based on the voltage levels in relation to a threshold voltageof each respective transistor of the plurality of first transistors. 25.The apparatus of claim 24 wherein the duty cycle is adjusted based on aratio of a pull down strength of the plurality of first transistors to apull up strength of the plurality of logic gates.